In current wireless local area network (WLAN) based on IEEE 802.11 standards, re-transmission is an important scheme to provide reliable communication. Re-transmission or not relies on acknowledgment (ACK) protocol. Upon successful reception of a frame of a type that requires acknowledgment, the destination station (STA) is required to respond with an acknowledgment if the frame check sum (FCS) of the received frame is correct after a short inter-frame space (SIFS) time interval. This technique is known as positive acknowledgment (ACK). On the other hand, if a reception failure happens at the destination STA, it does not send any ACK back to the source STA. If the source STA does not receive an acknowledgment frame within a given time period, for example, an ACKTimeout interval, then the source STA shall attempt to retransmit the failed frame. In WLAN based on IEEE 802.11 standards, the ACKTimeout interval is generally with a value of (sSIFSTime+aSlotTime+aPHY-RX-START-Delay) starting at the PHY-TXEND.confirm primitive.
FIG. 1 (prior art) illustrates a standard IEEE 802.11 ACK procedure in a wireless local area network 100. Wireless local area network 100 comprises a source station STA 101 and a destination station STA 102. At time t1, source STA 101 transmits a data packet 110 to destination STA 102. The destination STA 102 receives the entire data packet 110 at time t2, and decodes the data packet. If STA 102 decodes the received data packet 110 successfully, then the destination STA 102 sends an acknowledgement frame ACK 120 back to the source STA 101 at time t3. On the other hand, if a reception failure occurs and STA 102 cannot decode the received data packet 110 successfully, then the destination STA 102 does not send any ACK frame back to the source STA 101.
One problem of the aforementioned ACK scheme is that the source STA does not know causes of the failure transmission if no ACK is received. Therefore, the source STA does link adaptation blindly for subsequent retransmissions. One widely adopted scheme in re-transmissions is to use the lowest modulation and coding scheme (MCS). This scheme is too conservative and in most cases reduces the network efficiency. A solution is sought to assist link adaptation for re-transmission by the destination STA and improve the network throughput and efficiency.